1. Field of the Invention
The present invention relates to an imaging apparatus including a solid-state imaging device, such as a complementary metal-oxide semiconductor (CMOS) sensor, and an arranging method for the imaging apparatus.
2. Description of the Related Art
In a typical imaging apparatus using a CMOS sensor, light which passes through an optical system is subjected to photoelectric conversion with a photodiode included in a light-receiving unit formed on a semiconductor substrate. Then, electrons generated by the photoelectric conversion are accumulated and transmitted to an amplifier circuit, and a voltage output or a current output is obtained from the amplifier circuit.
A manner in which light enters such an imaging apparatus will be described below. FIG. 9 is a sectional view showing the structure of an example of a camera module including a CMOS sensor. FIGS. 10A and 10B are enlarged sectional views showing the structure of different pixels in a light-receiving unit of the CMOS sensor shown in FIG. 9. FIG. 10A shows a pixel at a position where light enters perpendicularly (denoted by a in FIG. 9), and FIG. 10B shows a pixel at a position where light enters at an angle (denoted by b in FIG. 9).
As shown in the figures, light 10 passes through a lens 12, an aperture 13, and a lens 14 placed in a lens barrel 11, enters each on-chip-lens 16 arranged on the surface of the CMOS sensor 15 for each pixel, is deflected by the on-chip lens 16 again, and is incident on a photodiode in a corresponding light-receiving section 17. Various kinds of wiring layers 18 are provided in the CMOS sensor 15.
As shown in FIG. 10A, in a central region of an imaging plane, light is substantially perpendicularly incident on the imaging plane. Therefore, light passes though the on-chip lens 16, and is directly incident on the light-receiving section 17. However, as shown in FIG. 10B, the incidence angle is increased as the distance from the center of the imaging plane increases, and light is incident on the imaging plane at a small angle relative to the imaging plane. Accordingly, not all of the light which passes through the on-chip lens 16 is incident on the light-receiving section 17, and some of the light reaches a region outside the light-receiving section 17. Therefore, the intensity of light incident on the light-receiving sections in a peripheral region of the imaging plane is reduced.
Next, the concept of an exit pupil in an optical system will be described below. FIG. 11 is a diagram showing an example of an optical system for a CMOS sensor 20. Two lenses 22 and 23 are disposed in front of an aperture 21, and a lens 24 is disposed behind the aperture 21.
An exit pupil refers to an image (virtual image) of the aperture made by the lens 24 positioned behind the aperture 21. In addition, an exit pupil distance refers to a distance between the imaging plane and the exit pupil.
Although the incidence angle in a peripheral region of the imaging plane can be reduced by using a lens having a long exit pupil distance, it becomes difficult to manufacture a thin lens module in such a case. In contrast, although a thin lens module can be manufactured by using a lens having a short exit pupil distance, the incidence angle in the peripheral region of the imaging plane increases in such a case.
In known structures, as shown in FIG. 12, each on-chip lens 31 is shifted away from the center of a corresponding light-receiving section 32 toward the center of the imaging plane by a distance proportional to the distance between the center of the imaging plane and the center of the on-chip lens 31 at a constant ratio in accordance with the exit pupil distance. The reason for this is to cause light with a large incidence angle to be incident on the light-receiving section with high efficiency. This is called pupil correction.
However, there is still a problem that the incidence angle is increased in the peripheral region of the imaging plane in a thin lens module. Therefore, there is a limit to collection efficiency obtained simply by shifting each on-chip lens at a constant ratio (refer to, for example, Japanese Unexamined Patent Application Publication No. 1-213079.
Accordingly, in known imaging apparatuses, the incident light intensity differs between the central and peripheral regions in the imaging plane of the CMOS sensor, and shading occurs in which the output from the CMOS sensor is large at the central region and small at the peripheral region.